Providing localized heat to a site in a patient's body has often been used to cauterize a lesion to stop bleeding. Localized heat can also be used to alter, remove, or destroy tissue in a patient's body. One example of such localized heating is the treatment of a bleeding ulcer. An endoscope is inserted through a patient's esophagus to view the bleeding site and direct an electric powered heating element to contact the site and cauterize the bleeding. Another example is the use of such heat to remove neoplastic pulmonary tissue.
Unfortunately, electric heating elements can be difficult to manipulate and generally heat up relatively slowly. The heating rate and maximum sustainable temperature is limited by the electric current available to the element. The available current in turn is limited by the size of the wires leading to the element. Wire size limits access to body sites for two reasons: larger wires cannot be inserted into small areas and increased wire size also means a loss of flexibility.
The electric current passing through the wires also limits the regions in the body in which such a device can be used. There is the threat of an electric shock to the patient and the generated field about the wires by flowing current can also have undesirable effects. One region where such electric currents and fields could possibly be life threatening is in the heart.
One proposal which heats the end of an endoscope to avoid dew forming on a window is shown in U.S. Pat. No. 4,279,246 to Chikama. That device heats the window to about body temperature to prevent dew formation. However, due to the design of the device, the heat generated on the window is limited to about body temperature and therefore could not be used to alter or destroy tissue.
Cardiovascular disease continues to be an ongoing problem, particularly in complex societies. It has been estimated that every year more than one-half million Americans die from cardiovascular disease. Another 3.5 million are believed to suffer some degree of incapacitation because of this disease. A particularly serious problem is the progressive blockage of a blood vessel by the collection or deposit of fatty material such as arteriosclerotic plaque. The collected material at first constricts the vessel, reducing blood flow to a relatively small channel. Eventually, blood flow can be obstructed completely.
Various devices and methods have been proposed in an attempt to deal with obstructed or constricted blood vessels. In one method, a balloon is positioned within the constricted channel and inflated, compressing the plaque into the vessel walls to widen the opening. This method is only available when the constriction in the blood vessel is not so severe that the remaining channel is too small for the deflated balloon. Compression of the plaque into the vessel walls is not possible where the plaque has become calcified and hard. Such a method is not even attempted in completely obstructed vessels. Applying radial stress to vessel wall also results in excessive and permanent deformation of this wall and subsequent loss of its integrity.
Accordingly, it would be desirable to provide a method and device which avoids the shortcomings of the prior art yet provides an effective means for delivering localized heat to a site within a patient's body. The heat provided by such a device can be used to stop bleeding or remove body tissue or material in a blood vessel, even a completely obstructed blood vessel. For such a device, the heat should be quickly developed without use of electrical current. Also, the device should be sufficiently small so that it can be directed into a patient's body cavity or lumen such as a blood vessel. It would also be desirable to provide rapid and accurate measurement of the heat produced. The present invention meets these desires.